The Borg line of products consists of a flexible, and uniquely modular series of high quality refractors with diameters ranging from 50mm to 150mm.
Borg M57/60 Extension Tube S (20mm long)
Borg M57/60 Extension Tube L (60mm long)
Borg M57/60 Extension Tube M (40mm long)
Borg M49.8 Extension Tube S (8.2mm long)
Borg M49.8 Extension Tube M (21.5mm long)
Borg M57/60 Extension Tube SS